Heterospecific aggression and dominance in a guild of coral-feeding reef fishes: The roles of dietary ecology and phylogeny

Background/Question/Methods

Competition is often conceptualized as being exploitative (indirect) or involving direct interference. However, most empirical studies of competition are phenomenological, focusing on quantifying effects of density manipulations, and most competition theory has characterized exploitation competition systems. The effects on resource use of traits associated with direct, interference competition has received far less attention. Aggressive, interference interactions are thought to require both resource overlap and the possibility of resource defense. Aggression is more likely to provide resource gains if directed toward competitors with shared resource requirements, and resource specialists are hypothesized to value their resources more highly than resource generalists. Here we combine quantitative estimates of dietary overlap and specialization to examine the relationship of dietary ecology to heterospecific aggression in a guild of corallivorous reef fishes. Further, we examine dietary overlap and specialization for phylogenetic signal, and test whether heterospecific aggression increases with phylogenetic similarity.

Results/Conclusions

Heterospecific aggression among butterflyfishes depends on a synergistic interaction of dietary overlap and specialization: aggression increases with dietary overlap for interactions between specialists, but not for interactions involving generalists. Moreover, behavioral dominance is a monotonically increasing function of dietary specialization. The strong, positive relationship of dominance to specialization suggests that heterospecific aggression may contribute to the maintenance of biodiversity where it promotes resource partitioning. Additionally, we find strong phylogenetic signals in dietary overlap and specialization, but not behavioral dominance, and that aggression is more common among more-closely related butterflyfishes. Our results support the use of phylogeny as a proxy for ecological similarity among butterflyfishes, but we find that direct measures of dietary overlap and specialization predict heterospecific aggression much better than phylogeny.